In machine tools, it is often necessary to provide precision indexing of a machine tool member. For example, in lathes, it often necessary to index a tool turret to discrete angular positions to present a new tool to the workpiece. Similarly, it is often necessary to provide indexing movement to a machine table, such as the rotary table on a milling machine, to present additional surfaces to the machine tool spindle when it is desired to machine these surfaces.
One common design of machine tool indexing mechanism simply utilizes two toothed coupling halves essentially consisting of two ring members having facial teeth disposed toward one another so that the two may be enmeshed to carry the indexable machine tool member relative to a fixed machine tool member. One very common such toothed coupling arragement is produced on machines generating a Curvic tooth form, (Registered Trademark of Gleason Works) which is well-known in the art. Many other tooth forms may be employed as well to obtain the degree of precision registration necessary in the coupling.
A common problem exists with the use of two multitooth coupling halves, which may readily be seen in that the coupling can be indexed only to increments which are multiples of the tooth spacing. For example, when using a 72 tooth coupling, having tooth spacing of 5.degree., one is limited to discrete index increments of 5.degree. or multiples thereof. A second problem exists in the use of a two-part coupling arrangement as described, in that axial movement must be provided to the one coupling half to separate the coupling prior to index. This requirement of separable coupling halves can be disadvantageous when one of the coupling halves supports a heavy machine member and thus requires great lifting power. Further, it is sometimes possible on movable machine tool members for chips to pack up between the relatively movable members.
A novel improvement in the area of toothed index coupling mechanisms is shown and described in U.S. Pat. No. 3,618,426, of Fisher, wherein three locating and locking elements are employed in the index mechanism. In the Fisher patent, a first coupling half having facial teeth is secured to a machine slide, and a second relatively movable coupling half having facial teeth, is mounted concentric to the fixed coupling half and rotatably movable relative thereto. The angularly movable coupling half carries an indexable machine member to discrete angular increments when indexed, and a third coupling half having facial teeth disposed towards the first and second coupling members, is moved into and out of meshing engagement with the fixed and rotatable coupling elements when indexing is desired. By this manner of design therefore, the indexable machine tool member need not have any axial movement relative to the fixed coupling half, since the third coupling element acts as a keying means and it alone is moved in an axial fashion relative to the fixed and rotatable coupling halves.
A similar impediment exists in the Fisher patent, as in the two-part index couplings, in that the indexable machine element and its associated coupling can only be moved to discrete angular increments corresponding to a whole tooth space on the fixed coupling element.
Applicant has obviated the difficulties inherent in the prior art devices by his novel design which employs coupling elements which permit fine resolution indexing of a machine tool member to descrete angular increments corresponding to a difference in tooth spacing of the relatively fixed and movable coupling elements.
It is therefore an object of the present invention to provide an indexing mechanism capable of fine resolution indexing of a machine tool member without axial movement of the member.